EP-3 Course- Transformer Tank

Transformer tank

Transformer tank is made of low-carbonic, structure steel which is easily welded and has good mechanical properties.
None-magnetic, rust proof (chrome) steel is used for the parts where connections of high bushings are placed.

Tank uses: 

  • To be the container for the oil 
  • To be a physical protection for the active part 
  • To be a support structure for accessories and control equipments 
  • To withstand the pressure from the atmosphere with a minimum deformations

Types of tanks: 
1-Tank and tank cover jointed with bolted connection (see fig.1)


Where the tank cover is a flat plate reinforced with ribs, or where the tank and the tank cover are welded construction.
This type is adjusted for road transportation on special vehicles or for railroad transportation when it is placed on a wagon.

2-Bell type tank (see fig.2)

This type has a construction reverse to the type above , the cover is designed as a bell and the lower part is either a flat plate or a sshollow vessel joined with the cover either with welded or bolted connection.
This type also designed for larger transformers because it enables opening of a transformer using crane with a lower load-bearing capacity since the bell of the tank weights is less than the active part of the transformer.

3-tank for railroad transportation (being a part of a train) (see fig.3)

This version of tank is generally used for larger transformers where dimensions and mass represent a limiting factor for road transportation. 
This type of tank requires special reinforcements such as suspensions on the train.

Conservator Tank 
The tank must be designed to permit the temperature dependent expansion of the oil, most often a separate expansion vessel is installed, also called “Conservator Tank”. 
Since the conservator is vented to the air the oil pressure in the transformer remains fairly constant and independent of the temperature. 
The air entering the conservator must be filtered and humidified to keep the good dielectric properties of the oil by getting the oil to be clean and has low moisture content, it is preferable in power transformers to use a diaphragm (see fig.4) in form of rubber sack that separates the oil in the conservator from the air.


Tank accessories: 
1- Tank bottom: a firm welded grid constructed of steel plates or profiles (see fig.5)

2-Pulling eyes (see fig.6)

3-Lifting hooks (see fig.7)

4-Oil sampling valves (see fig.8): the standard position of oil sampling valves is near the bottom with a possibility of taking oil samples from the bottom, middle and top of the tank. 

5- Earthing connections (see fig.9) : Two connections placed diagonally in the corner near the bottom of the tank.


6-Oil drain valves (see fig.10): used at the same way as filtering connections, placed diagonally near the bottom and the top of the tank.

7-Supports for transformer lifting (hydraulic jacks) (see fig.11).


8-Ladder (see fig.12): in the standard version, tanks are also provided with a ladder attached to them enabling an easy access to the transformer cover during assembly while making maintenance work. 


9-Wheels (see fig.13): on customer’s request, wheels can be fixed with bolts at the bottom of the tank with the possibility of rotating the wheels to move the transformer along the longitudinal or transversal axis. 

10- Others
  • openings enabling inspection of the tap changer and bushing connections as well as cooling system connections.
  • Flanges to secure the tightness of the tank which provided with grooves or stops preventing the seals from being exposed to excessive pressures, this seals are made of oil tight rubber of round or elliptic profile.

Method for filling oil in the tank: 
The tank must be evacuated in order to remove all air that would endanger the dielectric strength of the transformer insulation.

Methods of tank insulations from flux leakage
Due to the effects of large currents in and out of the transformer, there will be a leakage flux inside the tank, so we use inserts of non-magnetic materials around the high current bushings to reduce the risk of excessive heating. 

Tank lining with high conductive shields expels the flux from entering the tank wall, alternatively low reluctance material can be used to reduce the flux before entering into the tank walls.

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